<p>Objects which are pooled and potentially reused should not be used for synchronization. If they are, it can cause unrelated threads to deadlock
with unhelpful stacktraces. Specifically, <code>String</code> literals, and boxed primitives such as Integers should not be used as lock objects
because they are pooled and reused. The story is even worse for <code>Boolean</code> objects, because there are only two instances of
<code>Boolean</code>, <code>Boolean.TRUE</code> and <code>Boolean.FALSE</code> and every class that uses a Boolean will be referring to one of the
two.</p>
<h2>Noncompliant Code Example</h2>
<pre>
private static final Boolean bLock = Boolean.FALSE;
private static final Integer iLock = Integer.valueOf(0);
private static final String sLock = "LOCK";

public void doSomething() {

  synchronized(bLock) {  // Noncompliant
    // ...
  }
  synchronized(iLock) {  // Noncompliant
    // ...
  }
  synchronized(sLock) {  // Noncompliant
    // ...
  }
</pre>
<h2>Compliant Solution</h2>
<pre>
private static final Object lock1 = new Object();
private static final Object lock2 = new Object();
private static final Object lock3 = new Object();

public void doSomething() {

  synchronized(lock1) {
    // ...
  }
  synchronized(lock2) {
    // ...
  }
  synchronized(lock3) {
    // ...
  }
</pre>
<h2>See</h2>
<ul>
  <li> <a href="https://www.securecoding.cert.org/confluence/x/rQGeAQ">CERT, LCK01-J.</a> - Do not synchronize on objects that may be reused </li>
</ul>

